Re: async file i/o

[Havoc Pennington <hp redhat com>]

Michael Rothwell <rothwell holly-springs nc us> writes:
> David Helder wrote:
>
> > O_NONBLOCK should work.  E.g.:
> >   state->fd = open (state->pathname, O_RDONLY | O_NONBLOCK);
> >
> > Then you can use select() or create an IOChannel from the file handle and
> > use g_io_channel_add_watch().
>
> I just wrote a small program using glade to read a file from a floppy in
> 4096 byte chunks, using O_NONBLOCK and GIOChannel. It blocks. :(

If you use the main loop (g_io_channel_add_watch(), g_main_run() or
gtk_main()), then O_NONBLOCK isn't needed, because read() won't block
as long as at least one byte is available for reading; your GIOFunc
callback will only be invoked by the main loop if there's at least one
byte.

I think fread() on the other hand will always block, though I could be
wrong.

Of course the main-loop-async may not be what you want, if you want
threads then GIOChannel isn't going to get you anywhere.

Still, O_NONBLOCK should work I think, are you sure you are blocking
on the file descriptor? (see strace output) - maybe you are just
busy-looping by not checking for EAGAIN?

Havoc